Optical communication systems increasingly use wavelength-division multiplexing (WDM) and time- and wavelength-division multiplexing (TWDM) to increase bandwidth capacity. In a WDM passive optical network (PON), multiple optical data signals of different wavelength ranges or channels are combined as a single multiplexed optical signal and transmitted through a single optical fiber. In a TWDM PON, a WDM PON may be overlaid on top of a time-division multiplexing (TDM) PON. In other words, different wavelengths are multiplexed together to share a single feeder fiber, and each wavelength is shared by multiple users using time-domain multiple access (TDMA).
Optical network units (ONUS) that operate in WDM PONs or TWDM PONs may benefit from wavelength-tunable optical filters. For example, an ONU may employ an optical tunable filter in a receive path to receive signals from a selectable wavelength channel or in a transmit path to transmit signals in a selectable wavelength channel.